Polar Ice Accumulation from Volcanically Induced Transient Atmospheres on the Moon

Abstract

Water ice exists at the lunar poles, but its origin, abundance, and distribution are not well understood. One potential source of water to the poles is the volcanic outgassing of volatiles from the lunar interior and subsequent condensation of erupted water vapor as surface ice. We investigate whether volcanic outgassing is a viable source for the accumulation of lunar polar water ice. We construct a model that accounts for volcanic outgassing, atmospheric escape to space, and surface ice accumulation over the period of peak lunar volcanic activity (4–2 Ga) and map the resulting water ice distribution and abundance using current surface temperature data from the Lunar Reconnaissance Orbiter. Our model suggests that ∼41% of the total H2O mass erupted over this period could have condensed as ice in the polar regions, with thicknesses up to several hundreds of meters. The south pole accumulates roughly twice the ice mass of the north, and the southern deposits are thicker. Typical modeled eruptions generate collisional atmospheres with lifetimes of ∼2500 yr. However, these atmospheres are episodic and generally do not persist between eruptions. Roughly 15% of an atmosphere’s water vapor mass forms a frost on the lunar nightside, while the transient atmosphere persists. Our work suggests that the volcanically active period of the early Moon would have been punctuated by short-lived, collisional atmospheres that enabled the efficient sequestration of large quantities (8.2 × 1015 kg) of water ice at the poles and the temporary diurnal availability of water ice and vapor at all latitudes.